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Journal of Bacteriology, June 2008, p. 4121-4128, Vol. 190, No. 12
0021-9193/08/$08.00+0     doi:10.1128/JB.00123-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

The Xenorhabdus nematophila nilABC Genes Confer the Ability of Xenorhabdus spp. To Colonize Steinernema carpocapsae Nematodes

Charles E. Cowles and Heidi Goodrich-Blair^*

Department of Bacteriology, University of Wisconsin—Madison, Madison, Wisconsin 53706

Received 24 January 2008/ Accepted 24 March 2008

Members of the Steinernema genus of nematodes are colonized mutualistically by members of the Xenorhabdus genus of bacteria. In nature, Steinernema carpocapsae nematodes are always found in association with Xenorhabdus nematophila bacteria. Thus, this interaction, like many microbe-host associations, appears to be species specific. X. nematophila requires the nilA, nilB, and nilC genes to colonize S. carpocapsae. In this work, we showed that of all the Xenorhabdus species examined, only X. nematophila has the nilA, nilB, and nilC genes. By exposing S. carpocapsae to other Xenorhabdus spp., we established that only X. nematophila is able to colonize S. carpocapsae; therefore, the S. carpocapsae-X. nematophila interaction is species specific. Further, we showed that introduction of the nilA, nilB, and nilC genes into other Xenorhabdus species enables them to colonize the same S. carpocapsae host tissue that is normally colonized by X. nematophila. Finally, sequence analysis supported the idea that the nil genes were horizontally acquired. Our findings indicate that a single genetic locus determines host specificity in this bacteria-animal mutualism and that host range expansion can occur through the acquisition of a small genetic element.

Published ahead of print on 4 April 2008.

Present address: Department of Molecular Biology, Princeton University, Princeton, NJ 08544.